Low Frequency Noise in Strained Si Heterojunction Bipolar Transistors

The low frequency noise performance of strained Si heterojunction bipolar transistors (sSi HBTs) is presented for the first time. Conventional SiGe HBTs and Si bipolar junction transistors (BJTs), processed with strained Si devices, were also measured as a reference. It is found that a lower noise level is obtained in sSi HBTs for a given collector current, which is important for circuit applications, compared with either SiGe HBTs or Si BJTs. However, sSi HBTs exhibit greater low frequency noise compared with other devices at fixed base current. This is due to the presence of defects that are caused by the integration of the strain-relaxed buffer in the fabrication of sSi HBTs. The relationship between low frequency noise and defects is supported by material characterization.